Narathiwat Forensic Science Office Chief Pol Lt Gen Krajang Raknarong led experts to inspect the Super Department Store in Narathiwat provincial seat after the department store was hit by fire.
The fire has caused some Bt10 million in damages.
According to the initial investigation, the blaze was started on the cleaning supplies section located to the left end of the department store entrance. The fire spread to ready to wear clothes and stationary and quickly raged through the whole building.
Collection of evidence was very difficult, as the fire totally burned the goods and debris piled up in the building.
However, the police believed that the fire was caused by a five kilogramme explosive and may have been tied with a petrol bottle in order to make the fire spread quickly.
Narathiwat police inspector superintendent Pol Col Satanfah Wamasing has order the investigation team to check CCTV footage around the areas to track down the attackers.
The fire broke out at around 10pm and dozen of fire engines were mobilised to control the fire which took around one hour to extinguish.
The authorities believed that the assailant pretended to be a customer and placed the bomb inside the department store before triggering the explosive.
There were no reports of casualties from the incident.